Net Loss per Share - Reconciliation of Numerator and Denominator Used in Computing Basic and Diluted Net Loss per Share (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net loss	$ (21,397,791)	$ (13,958,408)
Accretion of stock issuance costs	(35,046)	(102,677)
Accretion of Series E warrant discount	(127,616)	(313,152)
Accretion of Series D and E redeemable convertible preferred stock dividends	(1,165,932)	(3,244,572)
Net loss attributable to common stockholders	$ (22,726,385)	$ (17,618,809)
Denominator:
Weighted-average common shares outstanding-basic and diluted	4,518,499	100,659
Net loss per share attributable to common stockholders, basic and diluted	$ (5.03)	$ (175.03)
Series E Warrants
Numerator:
Accretion of Series E warrant discount	$ (127,616)	$ (313,152)